#define  _CRT_SECURE_NO_WARNINGS
class Solution {
public:
    int takeAttendance(vector<int>& records) {
        int left = 0, right = records.size() - 1;
        while (left < right)
        {
            int mid = left + right >> 1;
            if (records[mid] == mid) left = mid + 1;
            else right = mid;
        }
        return records[right] == right ? right + 1 : left;
    }
};